High efficiency conversion of solar radiation into thermal energy

ABSTRACT

A high-efficiency solar radiation collection and conversion system is described. An array of evacuated collector tubes each includes two or more inner heat pipes that capture the solar energy and conduct it as heat through a condenser portion into a manifold that operates as part of a closed-loop circulation system. In another part of the loop, a heat exchanger transfers the heat into a hot-water holding tank or otherwise applies the heat energy in the circulating fluid.

REFERENCE TO RELATED APPLICATION

This application is a nonprovisional of, and claims priority to, U.S. Provisional Application No. 61/305,135, filed Feb. 16, 2010, with title “High Efficiency Conversion of Solar Radiation into Thermal Energy,” pending. The entire disclosure in that application is incorporated herein by reference as if fully set forth.

FIELD

This disclosure generally relates to the use of solar heat. More particularly, the disclosure relates to solar heat collectors having working fluid conveyed through the collector and having means to exchange heat between plural fluids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a solar radiation conversion system according to one embodiment.

FIG. 2 is a top section view of a header and array of solar collection tubes for use in the embodiment of FIG. 1.

FIG. 3 is a magnified section view of a header and part of an array of collection tubes used in the embodiment of FIG. 1.

DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to certain embodiments illustrated in the disclosure, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

Generally, with reference to FIG. 1, system 100 includes a solar collection subsystem 110, a closed-loop circulation system 115, and tank 130. Solar collection subsystem 110 receives incident solar radiation E and moves the heat energy into the fluid flowing through circulation system 115. That fluid circulates through tank 130, where heat is drawn out, and back to solar collection subsystem 110.

In particular, solar collection subsystem 110 includes collection tubes 112 (described further herein), header assembly 116, support members 114, and one or more legs 118 that support the other components of solar collection subsystem 110 at a desired angle and in a desired position. Each collection tube 112 includes a double-wall outer tube (a substantially transparent outer cylinder and an inner cylinder adapted to pass light and hold heat, fused together at the ends with evacuated space in between) that contains two or more inner “heat pipes,” which carry the heat energy up to the highest point in the tube. There the heat is transferred to recirculating fluid 128 (see FIG. 2) in header assembly 116. Pump 120 moves recirculating fluid 128 through closed-loop circulation subsystem 115, which includes pipe 122, header 217 (see FIGS. 2-3) in header assembly 116, pipe 124, tank 130, and pipe 126. Within tank 130, heat exchanger 132 pulls heat out of recirculating fluid 128 and into the water in tank 130. The heated water in the storage tank 130 is then available for many uses, as will occur to those skilled in the art, including without limitation domestic hot water, heated water for radiant floor heating, recovery water for boiler systems, commercial hot water systems, and other applications.

In other embodiments, tank 130 holds fluid other than water, which is likewise used as will occur to those skilled in the art. In still other embodiments, recirculating fluid 128 transports heat energy to any other load for using heat energy that will occur to those skilled in the art. In these various systems, recirculating fluid 128 may be a mixture of 70% propylene glycol and 30% water, or it may be any other fluid suitable for heat transport as will occur to those skilled in the art.

FIG. 2 illustrates an array 210 of collection tubes 212 that cooperate to capture solar energy for the system. As discussed elsewhere herein, each collection tube 212 connects with manifold 217 (within manifold assembly 214), where recirculating fluid 128 captures the heat. Recirculating fluid 128 enters manifold 217 through inlet 216 and exits through outlet 218, flowing through the rest of circulation subsystem 115 as discussed above. End caps 221 protect the ends of collection tubes 212 and hold collection tubes 212 in position. They may be made from plastic, metal, or other material as will occur to those skilled in the art.

FIG. 3 illustrates more detail about collection tubes 212 and their interface with manifold 217. In this embodiment, each collection tube 212 is a double-wall glass tube made of a transparent outer cylinder and an inner cylinder coated with a selective coating (such as AIN/AI) that features excellent solar radiation absorption and minimal reflection properties. The ends 213 of the cylinders are fused together as the space between them is evacuated at high temperature in order to create and maintain a vacuum gap between the cylinders.

The transparency of the outer cylinder allows light rays to pass through with minimal reflection. The inner cylinder absorbs radiation and reflects only minimal amounts thereof. The evacuated space between the inner and outer cylinders helps the efficiency of the collection subsystem in several ways, including but not limited to reducing the amount of radiant energy that is absorbed by matter in that evacuated space 224; reducing the overall mass of the system; and avoiding losses due to conduction of heat from the heat pipes 220 to the ambient air 226.

Within each collection tube 212, in the space inside the inner cylinder, are two or more heat pipes 220. Each heat pipe 220 in this embodiment is made of high-purity copper, containing only trace amounts of oxygen and other elements. These and other implementations of the invention will have different and additional advantages as will occur to those skilled in the art.

In operation, heat pipes 220 function to capture incident radiant energy as heat and transfer that heat to header 217. Each heat pipe 220 is evacuated, and a small quantity of purified water and/or other fluid (as will occur to those skilled in the art) is added. By evacuating the heat pipes 220, one lowers the temperature at which the fluid evaporates in the tube. In one embodiment, the heat pipes 220 have a boiling point of only 30° C. (86° F.), so when the heat pipe 220 is heated above that temperature, the fluid vaporizes. This vapor rapidly rises to the condenser 222 located at the top of the heat pipe 220. This condenser is inserted into header pipe 217. A mixture 228 of 70% propylene glycol and 30% water is pumped through the header 214, absorbing via condenser 222 the thermal energy harvested by the heat pipe 220. As this heat is drawn from the condenser, the vapor in inner tube 220 condenses in condenser 222 and returns to the bottom of the heat pipe 220 to repeat the process.

Even though heat pipe 220 is evacuated and the boiling point of the fluid inside has been reduced, the freezing point of that fluid is still the same as at sea level (which, in this embodiment, is 0° C. (32° F.)). Because the heat pipe 220 is located within the inner cylinder, protected from losses to ambient air 226 by the vacuum gap 224, brief overnight temperatures as low as −20° C. (14° F.) will not cause the heat pipes 220 to freeze. Plain water heat pipes may be damaged by repeated freezing. The water used in the heat pipes in the present system still freezes in cold conditions, but it freezes in a controlled way that does not cause swelling of or damage to the copper pipe.

The use of two or more heat pipes 220 within each collection tube 212 provides additional advantage over other designs. For example, having two or more heat pipes within each solar collection tube provides significantly greater density in the overall collection subsystem than other designs. Further, this aspect of the present design is complimentary to other techniques for improving capture of solar radiation in solar collection systems, and can be combined with techniques like using lenses or reflectors to concentrate the solar radiation before it is captured. Other radiation concentration techniques can be used with this system as will occur to those skilled in the art in view of this disclosure.

In various embodiments, two, three, four, or more heat pipes may be contained within each outer tube and connected to the closed circulation path via conductive heat transfer. In other embodiments, multiple collection manifolds receive heat from the condenser portions of the heat pipes, running (as a non-limiting example) in parallel through the manifold enclosure.

While the inventions have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that the preferred embodiment has been shown and described and that changes and modifications that come within the spirit of the invention are desired to be protected. 

1. A solar energy collection system, comprising: an elongated, substantially cylindrical, transparent outer tube comprising an outer cylinder and an inner cylinder, wherein the outer and inner cylinders are transparent and substantially axially concentric, the space between the outer and inner cylinders is evacuated, the ends of the outer cylinder form an air-tight connection with the corresponding ends of the inner cylinder such that the evacuated space remains evacuated, and one end of the outer tube is closed; a first and a second heat pipe, each comprising a collection portion and a condenser portion, the collection portion being substantially contained within the outer tube; a circulation path, comprising: a manifold in heat-conducting communication with an end of each of the first and second heat pipes; and a load for using heat energy.
 2. The system of claim 1, wherein the first and second heat pipes each: comprise a collection portion and a condenser portion, the condenser portion being the end in communication with the manifold; are evacuated; and contain a first fluid.
 3. The system of claim 1, wherein a second fluid passes through the circulation path.
 4. The system of claim 3, wherein the circulation path is a closed-loop path through which the second fluid is driven by a pump.
 5. The system of claim 3, wherein the second fluid comprises water.
 6. The system of claim 1, wherein at least a portion of the first and second heat pipes are made of copper.
 7. The system of claim 1, wherein the first fluid comprises water.
 8. The system of claim 1, wherein the outer and inner cylinders are made of borosilicate glass.
 9. The system of claim 8, wherein the inner cylinder is coated with AIN/AI.
 10. The system of claim 1, further comprising a third heat pipe that is contained within the outer tube and is in heat-conducting communication with the manifold.
 11. A method of manufacturing a solar collector, comprising: placing two or more heat pipes, each having a collection portion and a condenser portion, and each being adapted to move heat from the collection portion to the condenser portion, in heat-transfer communication with a manifold; and placing an evacuated tube around the collection portion of the two or more heat pipes, where the evacuated tube comprises an inner cylinder and an outer cylinder, the outer cylinder being substantially transparent, the inner cylinder defining an internal volume that contains the two or more heat pipes, and the ends of the inner cylinder a the outer cylinder being sealed to define an evacuated space; such that the condenser portion of each heat pipe is elevated in relation to the collection portion.
 12. The method of claim 11, further comprising connecting the manifold to a load for using heat energy in a closed circulation path, wherein a second fluid passes through the circulation path.
 13. The method of claim 12, wherein the circulation path is a closed-loop path through which the second fluid is driven by a pump.
 14. The method of claim 12, wherein the second fluid comprises water.
 15. The method of claim 11, wherein at least a portion of the first and second heat pipes are made of copper.
 16. The method of claim 11, wherein the first fluid comprises water.
 17. The method of claim 11, wherein the outer and inner cylinders are made of borosilicate glass.
 18. The method of claim 17, wherein the inner cylinder is coated with AIN/AI.
 19. The method of claim 11, further comprising a third heat pipe that is contained within the outer tube and is in heat-conducting communication with the manifold. 